Selective Determination of Oxalate with a Ruthenium(II) Complex/Nafion-Modified Electrode Combined with a Carbon Dioxide Sensor

A tris(2, 2′-bipyridine)ruthenium(II)/Nafion-modified Pt gauze electrode, where CO2 was generated by oxidation of substrates, was combined with a CO2 sensor. The combined sensor responded most effectively to oxalate among the organic acids examined. The response to oxalate was enhanced by use of a doubly-piled, modified Pt gauze electrode. The most suitable applied potential was +0.95V vs. Ag/AgCl; the stationary response was attained in 10min after the potential application. The response to 0.5mM oxalate was reproducible within 3% on 10 repeated runs and remained virtually unchanged over 10 days. The calibration curve for oxalate was linear in the concentration range of 0.1 to 5mM, and the detection limit was 0.05mM (S/N=3).